Grinding mill discharge



March 14, 1944. s MlLLER 2,344,162

GRINDING MILL DISCHARGE Filed NOV. 26, 1940 Smmrs L. MILLER INVENTOR.

izfa wi ATTORNEK Patented Mar. 14, 1944 UNITED STATES PATENT OFFICE GRINDING MILL DISCHARGE Starks L. Miller, Denver, Colo., assignor, by mesne assignments, to Richard W. Marland, Denver,

2 Claims.

This invention relates to improvements in grinding mills, and more particularly relates to the discharge control of such a mill.

A principal object of the invention is to improve th efiiciency and speed up the discharge of ground material from such a mill, in order to increase the efiiciency of the grinding.

Another object is to secure a better efiiciency in the separation of the ground product of such a mill, passing the finished product out of the mill and returning the oversize to the grinding chamber for further reduction.

A further object is to provide such improved discharge-end construction for a ball mill or the like, that may be installed upon such mills that are already in use.

Another object of the invention is to provide flexibility of design that will permit the use of an annular peripheral opening of any desired width to meet the demands of any or all operating conditions. This feature is of particular importance when extremely small balls are used as a grinding medium.

Another object of the invention is to insure free, unobstructed passage of pulp through the annular peripheral discharge opening from the grinding chamber into a separate annular passage, from which the pulp is directed either by gravity or by diversion lugs or by both, to the sizing means.

Other objects and advantages reside in details of design and construction which will be more fully disclosed in the following description and in the drawing wherein like parts have been similarly designated and in which:

Figure 1 is a fragmentary side elevation partially in section, illustrating the discharge end of a ball mill that embodies the present inventive concept;

Figure 2 is a fragmentary sectional view illustrating certain details that appear in Figure 1;

Figure 3 is an end elevation, partially in section, of the discharge end of the ball mill of Figure l;

Figure l is a fragmentary circumferential section taken along line 4-4 of Figure 3; and

Figure 5 is a side elevation of a discharge sec tion, constructed in accordance with this invention.

In order to disclose operative reductions to practice of the present inventive concept, the accompanying drawing will be described in detail. However, these illustrations are intended to set forth typical examples and therefore they should tations to this invention, the scope of which is, in reality, measured by the appended claims.

Referring first to Figure 1, reference character 52 denotes the cylindrical shell of a typical ball mill in which are a plurality of attrition members I 3. This mill is provided with a trunnion l4 upon which it is journalled for rotation in suitable bearing structure l5.

The trunnion i4 is hollow as shown at It, and is provided with an outwardly flared discharge hell I I through which the finished product passes.

An nd liner element I8 is of dish-shape cross section, thus tending to roll the balls or attrition members I3 inwardly of the mill. End liner I8 is supported upon a conical disk 59 which has an inwardly extending flange 20 that facilitates such support, and an outwardly extending flange 2|.

he shell liners of the mill are indicated by reference character 22 and terminate in an inwardly extending rib 23. The perimeter of the end liner element i8 is generally circular and is spaced away from the inwardly projecting flange 23 on the shell liners, thus providing an unobstructed peripheral annular discharge 24 for the discharge of ground products from the mill shell ii. In cross section, the peripheral annular discharge 25 increases in width in the direction of discharge from the mill, thus to prevent clogging, in that any material that can enter said discharge 24 can pass completely therethrough.

The construction shown in the drawing may be incorporated in the original design of a grinding miil. However, a feature of this invention of particular value is the replaceability by the discharge unit of this invention of the usual head at the discharge end of a conventional ball mill or the like, particularly a ball mill already in service. For this purpose, it is necessary only to slide successive sections 28 into the mill, as from the position of the section 28 of Figure 5 relative to the ball mill as shown in Figure 4, and then suitably secure the sections to the remainder of the ball mill, as by bolts. Thus, a ball mill already in service may be readily modified to possess the attributes and advantages of this invention.

In order to provide entirely free continuous peripheral discharge opening 24, another annular passage 124, Figure 1, is provided immediately on the discharge side of said peripheral opening 24. Further details of this annular passage I24 are clearly shown in Figure 4. The material flowing through peripheral opening 24 takes the course shown by the arrows.

In the form shown in Figure 4, all the material not be constr ed to xpres r o imp y ny limlthat enters the annular passage I24 ahead of the discharge units is directed to the grates 25 by diversion lugs I25 as shown. The material that enters the annular passage I24 to the rear of a diversion lug flows rearwardly through the passage and is directed to .the following discharge unit by the following diversion lug. It is readily seen that by providing the annular passage I24, the ground material discharges freely from the mill through the annular peripheral opening 24 which, therefore, cannot become blocked and is always open.

In my Patent No. 2,079,221, Figure 3, it will be noted that the peripheral discharge opening feeds only into the spaces between the discharge conduits. Material in the grinding chamber and opposite the discharge conduits that would otherwise have free access to the discharge is held in the grinding chamber until the space between the following conduits is presented. Because of this construction, actual relative efiectiveness of the mill discharge is determined by the ratio of area of the peripheral opening feeding into the space between conduits, to the area of the peripheral opening adjacent the conduits.

In the case of a long overflow mill of small diameter and where large tonnage is handled, it can readily be seen that because of a small diameter, the circumference of the peripheral opening is necessarily limited.

For the requirements as mentioned, the only way to increase the area would be to widen the peripheral opening, which, in the case Where small balls are used, cannot be done beyond a certain point without admitting too large a percentage of small balls into the discharge system.

With the present construction, approximately 100% more effective discharge can be had, which in turn means that the amount of ore or pulp that can be handled is nearly doubled.

It is manifest that ground ore or pulp that passes through annular peripheral discharge opening 24 into annular passage I24, but which is too large to pass through grates 25, will be passed along conduits 21, Figure 1, and thus be returned to the grinding chamber within the shell I2.

More briefly stated, the present improvement comprises an annular passage I24 in a position to receive ground ore or pulp discharged through an annular peripheral discharge opening 24, together with discharge grates 25, in conductive communication with the annular passage I24 and in certain forms of construction, diverting lugs I25 for directing ground ore or pulp toward the discharge grates 25. These features are, of course, used in combination with means for returning oversize material to the interior of the grinding chamber for further reduction. While the discharge assembly illustrated in Figure l, in most instances, would be a part of a specially built mill using such features, individual head sections may be built for mills already in use and bolted or otherwise fastened against the flange on the shell I2, as a substitute for the original head and associated discharge trunnion of such mill.

What I claim and desire to secure by Letters Patent is:

1. In a rotary grinding mill, inclusive of a shell having a discharge trunnion and liners for the shell, the improvement which comprises a hollow head member at the discharge end of the mill, end liners supported thereon having their peripheries in spaced relation to the ends of the shell liners to form therewith a continuous peripheral discharge passage from the mill, a series of individually removable hollow grate members radiating from the discharge trunnion within the hollow head in spaced relation to the end liners, and a laterally disposed diversion lug in the space between each grate member and the peripheral passage for directing material from the passage onto each grate, the interior of the grate members communicating with the discharge passage through the trunnion and the exterior surface thereof being arranged to return oversize to the mill.

2. In a rotary grinding mill, inclusive of a shell having a discharge trunnion and liners for th shell, the improvement which comprises a hollow head member at the discharge end of the mill, end liners supported thereon having their peripheries in spaced relation to the ends of the shell liners to form therewith a continuous annular discharge passage from th mill, a series of hollow grate members radiating from the discharge trunnion within the hollow head in spaced relation to the end liners. and a diversion lug in the space between each grate member and the adjoining end liner disposed at an inclination to the axis of rotation of the shell to direct material from the passage onto the grate, the interior of each said grate member communicating with the discharge passage through said trunnion and the exterior surface thereof being arranged to return oversize to the mill.

STARKS L. MILLER. 

